Factors affecting the rates of arsine evolution and arsenical mineralization in soil.

摘要

Effects of soil moisture, temperature, arsenic compounds, concentration of As, and cellulose addition on arsine evolution and demethylation of organic arsenicals were studied in Sacramento silty clay amended with As and incubated for 70 days. Volatile arsines were not detected over a gamma radiation sterilized soil, suggesting that arsine evolution in soil is a microbial process. When 100 mg As kg{dollar}sp{lcub}-1{rcub}{dollar} soil as sodium cacodylate was incorporated into the soil, the maximum arsine evolution occurred at a soil moisture level of 350 mg H{dollar}sb2{dollar}O kg{dollar}sp{lcub}-1{rcub}{dollar} (around {dollar}-1/3{dollar} bar) between 0-50 days and at a level of 250 mg H{dollar}sb2{dollar}O kg{dollar}sp{lcub}-1{rcub}{dollar} soil after 50 days. Total arsine production was higher at 25{dollar}spcirc{dollar}C than at 5{dollar}spcirc{dollar}C. At 5{dollar}spcirc{dollar}C, a relatively low and constant arsine evolution rate occurred, suggesting zero order kinetics. Biodegradation kinetics models were fit the data at 25{dollar}spcirc{dollar}C. The Monod model with growth and the two-compartment model gave the best fit. Total arsine production from soil amended with at rates of 100 mg As kg{dollar}sp{lcub}-1{rcub}{dollar} soil followed the order: sodium cacodylate (CA) {dollar}>{dollar} monomethylarsonic acid (MMAA) {dollar}>{dollar} sodium arsenite {dollar}>{dollar} sodium arsenate. Arsine evolution increased linearly with soil cacodylate concentration in the range of 0-100 mg As kg{dollar}sp{lcub}-1{rcub}{dollar} soil (R{dollar}sp2{dollar} = 0.99). Cellulose addition (0-5%, w/w) enhanced arsine production linearly (R{dollar}sp2{dollar} = 0.99).; Demethylation of CA increased as soil moisture increased from 50 to 550 mg H{dollar}sb2{dollar}O kg{dollar}sp{lcub}-1{rcub}{dollar} soil. More CA was demethylated at 25{dollar}spcirc{dollar}C than at 5{dollar}spcirc{dollar}C. The percentage of CA demethylated decreased as its initial concentration increased. Cellulose addition depressed CA demethylation indicating preferential microbial utilization of cellulose over CA. The rate of MMAA demethylation was lower than that for CA under the same conditions. The overall percentage of CA and MMAA demethylated after 70 days was much higher (3-87%) than arsine evolution (0.001-0.4%).; An experimental data based model was developed to predict the fate of soil arsenicals. Arsenic transformations were assumed to follow first order kinetics. The rate coefficients were calculated based on the arsenic species concentration measured after 70 days of incubation. The model predicts that degradation of CA over two years results in 99.8% conversion to arsenate and {dollar}<{dollar}0.2% evolution as arsines. Arsenic will accumulate in the soil from arsenical usage.